1. Field of the Invention
The present invention relates to a recording medium supplying device and an image forming apparatus.
2. Description of the Related Art
In image forming apparatuses such as copying machines, printers, facsimiles, or multifunction peripherals (MFPs) thereof, a sheet feeding device that supplies paper, an OHP film, or the like, one by one has been known. As the sheet feeding device, there is the following air separation sheet feeding device. That is, the air separation sheet feeding device blows air to pieces of paper in a bundle form that are mounted on a tray in a stacked state so as to make the pieces of paper (recording media) float and separate them from one another while flicking through the pieces of paper. Then, the air separation sheet feeding device makes paper at an uppermost position adsorb to an adsorption belt with a suction force and conveys the paper. As conventional air separation sheet feeding devices, there are air separation sheet feeding devices as disclosed in Japanese Patent Application Laid-open No. 2001-247229 and Japanese Patent Application Laid-open No. 2007-45630, for example.
FIG. 12 illustrates a schematic configuration of the above-described air separation sheet feeding device.
An air separation sheet feeding device 301 as illustrated in FIG. 12 includes a tray 302, a front blower 303 and a side blower 304, and an adsorption belt 305. A plurality of pieces of paper P are mounted on the tray 302. The front blower 303 and the side blower 304 blow air to upper front ends and upper side ends of the mounted pieces of paper P, respectively. The adsorption belt 305 adsorbs and conveys the mounted pieces of paper P one by one. Front end surfaces of the pieces of the paper P are made to hit a front fence 306 as a reference surface and are aligned so as to match with the size of the paper P on the tray 302.
The paper P is supplied on the air separation sheet feeding device 301 in the following manner. That is, air is blown onto a bundle of the pieces of paper P mounted on the tray 302 from the front blower 303 and the side blower 304, at first. With the air, the air is fed to between the pieces of paper P so as to make the pieces of paper P float to a height h of the adsorption belt 305 while flicking through the pieces of paper P. Then, paper P1 at an uppermost position is made to be adsorbed to the adsorption belt 305 among the floating pieces of paper. The adsorption belt 305 rotates in this state, so that the paper P1 is conveyed to an image forming unit (not illustrated) and image formation is performed.
Furthermore, each of the air separation sheet feeding devices as described in Japanese Patent Application Laid-open No. 2001-247229 and Japanese Patent Application Laid-open No. 2007-45630 includes an upper surface position detecting unit that detects a position of an uppermost surface of the mounted paper. As the upper surface position detecting unit, there is the following upper surface position detecting unit including an actuator 310 and a swing detecting sensor 311 as illustrated in FIG. 12, for example. The actuator 310 is configured to abut against an uppermost surface of a paper bundle and be capable of swinging. The swing detecting sensor 311 detects swinging of the actuator 310. An attachment position of the actuator 310 is provided in the vicinity of the adsorption belt 305 such that a desired distance h is continued to be kept with stable accuracy regardless of sizes of the paper P.
In this case, if the paper is supplied and the height of the paper bundle becomes lower, the actuator 310 swings therewith. Then, the swing detecting sensor 311 detects a swing amount of the actuator 310. A pushing-up unit (not illustrated) lifts a bottom plate of the tray 302 based on the detected signal, so that the height h (distance) from the upper surface of the paper bundle to the adsorption belt 305 is controlled to be constant.
On the actuator 310 of the upper surface position detecting unit as illustrated in FIG. 12, a roller 312 on a tip of the actuator 310 makes contact with the upper surface of the paper bundle with a constant pressing force all the time regardless of types of paper. However, in an image forming apparatus such as a copying machine, not only plain paper and recycled paper but also art paper and coat paper on which coating processing has been performed on surfaces thereof, no-carbon paper, and the like are available. Surfaces of these types of paper are easy to be scratched in comparison with the plain paper and the recycled paper. Therefore, a mark of the roller 312 is left with the pressing on the upper surface of the paper when the height of the paper is detected, resulting in deterioration of quality of output paper.
In particular, in a device in which a roller is separated temporarily from an upper surface of paper every time air is blown onto the paper, as described in Japanese Patent Application Laid-open No. 2011-73864, a collision force of the roller against the upper surface of the paper becomes larger and a mark of the roller is easy to be left on the paper when abutment and separation of the roller are repeated at high speed in order to convey the paper at high speed.
In order to solve the problem, it can be considered that the pressing force on the upper surface of the paper is set to be weaker. However, if the pressing force is set to be weaker, when rigid paper such as a cardboard is fed, an upward force with the rigidity of the paper overcomes the pressing force on the upper surface of the paper and there arises a risk that the upper surface position of the paper cannot be detected accurately. Moreover, when a hard cardboard is used, there arises a problem that collision noise is generated when the roller 312 on the tip of the actuator 310 abuts against the upper surface of the paper in some cases.
Therefore, there is a need to provide a recording medium supplying device that detects a height of paper reliably regardless of types of paper (types of recording medium) and conveys the paper reliably, and can prevent damage on the paper and generation of scratches and collision noise when the height of the paper is detected.